Method for fabricating a concrete slab in a substantially horizontal slip casting process and apparatus

Abstract

The invention relates to a method for fabricating a concrete slab (100) with an elongated channel (103) by using a digging tool (120) which removes unhardened concrete from a concrete slab by moving the digging tool in a digging direction (A) and rotating a blade assembly (124, 126) to scrape away a layer of unhardened concrete using the outer peripheral edges (124A, 126A) of the blade assembly and sideways pushing by using pushing sides (124B, 126B) of the blade assembly unhardened concrete towards the first end or the second end by rotating the blade assembly around an axis of rotation (122C). The blade arrangement moves the loosened unhardened concrete along an inner surface of a guide plate (130) into the direction of a collection chamber (160) of a discharge arrangement (170) by rotating the pushing sides (124B, 126B) around the axis of rotation.

Description

[0001] METHOD FOR FABRICATING A CONCRETE SLAB IN A SUBSTANTIALLY HORIZONTAL SLIP CASTING PROCESS AND APPARATUS

[0002] TECHNICAL FIELD

[0003] The invention relates to a method for fabricating a concrete slab provided with an elongated channel in a substantially horizontal slip casting process. More particularly, the invention relates to a method for fabricating hollow-core slabs.

[0004] BACKGROUND

[0005] A method for providing recesses in a surface of a concrete element is known from EP1134061. The method comprises the steps of cutting unhardened concrete to be removed, from the surface of an unhardened concrete element by means of cutting elements, in a tooling direction substantially parallel to the surface of the concrete element, discharging the unhardened concrete cut from the concrete element, and grinding the unhardened concrete cut from the concrete element. The unhardened concrete is reduced by rotating cutter blades into small cement particles. Water is fed to an area surrounded by the cutter blades and a liquid mass of cement, cement particles and water is formed. The liquid mass formed is pumped out, which requires a lot of energy. In addition the liquid mass formed cannot be reused immediately and thus requires storage space.

[0006] FR1416393A discloses a method for machining cellular structure materials obtained through casting in molds. The method involves milling the surface of the hardened material using cutters, similar to the consistency of putty, in order to remove the material in small slices and eliminate it without further contact with the machined surface. Subsequently, the waste is immediately ground and diluted into a fluid slurry that is either evacuated or reintroduced into the next casting process.

[0007] JP H08 302612 A discloses a concrete surface forming machine with wheels. Its machine body is fitted with screw blades, a trowel for formation of concrete surface, a vertical moving means to move the blades and trowel in the vertical direction, a transporting mechanism for concrete, and a hopper for storing the concrete. The screw blades 20 are composed of left blades and right ones which are driven individually, and the concrete 12 is raked together toward the center about the direction across the width of the machine body with regular rotation of the blades and scattered to the left and right with their reverse rotation. US6154988A disclosed a machine for digging under pipes. The machine comprises left and right end effectors. The end effectors are each made in the shape of a mount which is attached to the frame. These end effectors also comprise a cylindrical endless-screw-type driving cutters as well as a cylindrical blade attached to the mount coaxially behind the cutter. The depth of side trenches is made to be larger than the depth of the trench bottom which will be formed after passage of the claimed machine with formation of side pits. The driving cutters together with the cylindrical blade work the soil under pipeline and removes it into the side pits.

[0008] SUMMARY

[0009] It is an object of the invention to provide an alternative method for fabricating a concrete slab provided with an elongated channel, which overcomes at least one disadvantage of the known method.

[0010] According to the invention, this object is achieved by a method having the features of Claim 1. Advantageous embodiments and further ways of carrying out the invention may be attained by the measures mentioned in the dependent claims.

[0011] According to an aspect of the invention, there is provided a method for fabricating a concrete slab in a substantially horizontal slip casting process, in which method concrete mix is fed into a mold through a delimited cross section moving progressively in the casting process so as to form a concrete product of a desired shape. The method comprises the actions, a) loosening unhardened concrete to be removed from the surface of an unhardened concrete element by means of a digging tool to obtain loosened unhardened concrete, wherein the digging tool moves in a digging direction substantially parallel to the surface of the concrete element, b) discharging loosened unhardened concrete from the concrete element to form an elongated channel with a width determined by the digging tool. The digging tool comprises: a drive shaft having an axis of rotation and a drive direction around the axis of rotation. A blade assembly is attached to the drive shaft between a first end and second end of the drive shaft. The blade assembly comprises two or more blade arrangements attached to the drive shaft. The blade arrangements provide outer peripheral edges configured to scrap unhardened concrete away and provide pushing sides configured to move unhardened concrete in the direction of the first end or the second end when the drive shaft is rotating in the drive direction. The digging tool further comprises a guide plate extending from the first end to the second end configured to guide loosened unhardened concrete to a collection chamber of a discharge arrangement. The method further comprises the actions: c) moving the digging tool in a digging direction, d) rotating the drive shaft around the axis of rotation in the drive direction, e) loosening unhardened concrete by simultaneously making a cut in the unhardened concrete by the outer peripheral edges and pushing unhardened concrete by pushing sides towards the first end or the second end by rotating the blade assembly around the axis of rotation; f) moving loosened unhardened concrete along an inner surface of the guide plate into the direction of the collection chamber of a discharge arrangement by rotating the pushing sides around the axis of rotation.

[0012] These features provide a method for fabricating concrete slabs in a substantially horizontal slip casting process which does not require water to discharge to loosened unhardened concrete from the channel formed in the concrete slab. As a result, the method of making channel is cleaner than when water is used. Furthermore, as no water is used, when digging the channel, the composition of the concrete forming the walls is not changed. Consequently, the characteristics of the concrete, such as strength, are minimally changed. Furthermore, as no material is added to the loosened unhardened concrete could be fed directly to the concrete mix supply arrangement of the mold. Consequently, no storage space is needed to store the loosened unhardened concrete. Furthermore, to transport the loosened unhardened concrete any known transports system may be used, such as movable containers, conveyer belts or auger screw conveyor. Another advantage of the combined scraping and pushing action to dig the channel is that force to rotate the blade arrangement is less dependent on the angle of rotation of the drive shaft. As a result, a motor to drive the digging tool is loaded more evenly, improving the lifetime of the motor.

[0013] In an embodiment, the blade assembly comprises at least one cylindrical rotation area around the drive shaft provided with an end part of a pushing blade which is configured to push loosened unhardened concrete in the direction of the first end of the drive shaft and an end part of a pushing blade which is configured to push loosened unhardened concrete in the direction of the second end. The method further comprises moving loosened unhardened concrete in the at least one cylindrical rotation area alternately to the first end and to second end of the drive shaft. This feature ensures that when scraping away unhardened concrete in the area when the end parts overlap, the structure of the unhardened concrete that is left behind is less damaged, leaving the local properties of the final cured concrete virtually unaffected.

[0014] In an embodiment, the blade arrangement comprises: a first blade arrangement and a second blade arrangement attached to the drive shaft between a first end and second end of the drive shaft. The first blade arrangement extends from the first end into the direction of the second end, providing an outer peripheral edge configured to scrap unhardened concrete away and providing a pushing side configured to move loosened unhardened concrete in the direction of the second end when the drive shaft is rotating in the drive direction. The second blade arrangement extends from the second end into the direction of the first end, providing an outer peripheral edge configured to scrap unhardened concrete away and providing a pushing side configured to move loosened unhardened concrete in the direction of the first end when the drive shaft is rotating in the drive direction. The method comprises: moving loosened unhardened concrete away from the first end by rotation of the first blade arrangement around the axis of rotation; and moving loosened unhardened concrete away from the second end by rotation of the second blade arrangement around the axis of rotation. These features allow the loosened unhardened concrete to be collected in a limited area along the drive shaft and disposed of in a targeted manner.

[0015] In an embodiment, the blade assembly comprises helical shaped blades. This feature has the advantage that when a front end of the helical shaped blade hits the upper surface of the unhardened concrete slab to loosen unhardened concrete, the forces acting on the outer peripheral edge is relative small and increases gradually with rotation of the helical shaped blade around the axis of rotation. As soon as the back end of the helical outer peripheral has been in contact the upper surface of the slab, the total scraping force acting on the helical shaped blade will decrease. Furthermore, the fast rotational movement of the outer peripheral edge is converted into a slower lateral scraping movement over a wide range of rotation of the drive shaft, making the force required to rotate the blade assembly less dependent on the angular position of the drive shaft. These advantages improve the lifetime of a motor driving the driving shaft as it is gradually loaded heavier and lighter, and loaded shock-wise.

[0016] In an embodiment, a blade arrangement comprises multiple blade elements configured to push loosened unhardened concrete towards the first end or the second end of the drive shaft. This feature allows the blade arrangement to scrape unhardened concrete more than once in one revolution of the drive shaft.

[0017] In an embodiment, the two or more blade arrangements are provided with a V-shaped outer edge and a first pushing side configured to move loosened unhardened concrete toward the first end and a second pushing side configured to move loosened unhardened concrete in toward the second end when the drive shaft is rotating in the drive direction. This feature also has the advantage that when a blade arrangement with V- shaped outer edge start to loosen unhardened concrete, the greatest force is not acting on the blade arrangement when it hits the top surface of the concrete slab to scrape away unhardened concrete but gradually increases until the V-shaped outer edge is fully in contact with unhardened concrete of the slab.

[0018] In an embodiment, the digging tool further comprises a first circular disc attached to the first end and a second circular disc attached to the second end. The method further comprises: protecting the side walls of the elongated channel from being damaged by concrete parts jumping around between rotating pushing blades by the first and second circular disc. These features allow providing an elongated channel with a qualitatively good and uniform sidewall structure.

[0019] In a further embodiment, the peripheral edge of the first and second circular disc is located at a distance from the axis of rotation that is smaller than the distance between the outer peripheral edge of blade arrangements and the axis of rotation of the drive shaft. As a result, the circular discs have no digging function and will be less subject to wear.

[0020] In a further embodiment, a blade arrangement abutting the first circular disc and having a pushing side configured to move loosened unhardened concrete in the direction of the second end comprises a protrusion which is located in a plane defined by the circular disc. As a result, the protrusion mainly performs the function to dig the sidewall of an elongated channel. Consequently, the circular disc will be less subject to wear. In a more specific embodiment, the protrusion is located exterior the first circular disc. As a result, the circular discs have no digging function and will be less subject to wear.

[0021] In an embodiment, the guide plate comprises an opening providing a passage for discharging loosened unhardened concrete from the digging tool. The method further comprises: moving loosened unhardened concrete along the guide plate to the opening to discharge loosened unhardened concrete from the digging tool by rotation of the blade assembly around the axis of rotation.

[0022] In an embodiment, the method comprises: moving loosened unhardened concrete along the guide plate to discharge loosened unhardened concrete from the digging tool by rotation of the blade assembly around the axis of rotation in a collection chamber of a discharge arrangement located in front of the digging tool. This feature has the advantage that if loosened concrete happens to fall next to the discharge arrangement positioned before the digging tool and thus on the top surface of the slab, this concrete will once again pass through the digging tool to get it into the collection chamber of the discharge arrangement. As a result, after digging the channels, there will be less loosened concrete on the slab.

[0023] According to another aspect of the invention, there is provided for providing an elongated channel in a surface of an unhardened concrete element, comprising all technical features of a digging tool according to any of the claims 1 - 13

[0024] It is an object of the invention to provide a digging apparatus configured for executing the alternative method for fabricating a concrete slab provided with an elongated channel, which overcomes at least one disadvantage of the known method.

[0025] According to the invention, this object is achieved by a digging apparatus having the features of Claim 15. Advantageous embodiments and further ways of carrying out the invention may be attained by the measures mentioned in the dependent claims.

[0026] According to an aspect of the invention, there is provided a digging apparatus comprising a drive shaft, a blade assembly and a guide plate. The drive shaft has an axis of rotation and a drive direction around the axis of rotation. The blade assembly is attached to the drive shaft between a first end and second end of the drive shaft. The blade assembly comprises two or more blade arrangements which are attached to the drive shaft. The blade arrangements provide outer peripheral edges configured to scrap unhardened concrete away and pushing sides configured to move unhardened concrete in the direction of the first end or the second end when the drive shaft is rotating in the drive direction. The guide plate extends from the first end to the second end and is configured to guide loosened unhardened concrete to a collection chamber of a discharge arrangement.

[0027] In an embodiment, the blade assembly comprises at least one cylindrical rotation area around the drive shaft provided with an end part of a pushing blade which is configured to push loosened unhardened concrete in the direction of the first end of the drive shaft and an end part of a pushing blade which is configured to push loosened unhardened concrete in the direction of the second end.

[0028] In an embodiment, the blade arrangement comprises a first blade arrangement and a second blade arrangement both attached to the drive shaft between the first end and second end of the drive shaft. The first blade arrangement extends starting from the first end into the direction of the second end, and provides an outer peripheral edge configured to scrap unhardened concrete away and further provides a pushing side configured to move loosened unhardened concrete in the direction of the second end when the drive shaft is rotating in the drive direction. The second blade arrangement extends starting from the second end into the direction of the first end, providing an outer peripheral edge configured to scrap unhardened concrete away and provides a pushing side configured to move loosened unhardened concrete in the direction of the first end when the drive shaft is rotating in the drive direction

[0029] In a further embodiment, the first blade arrangement and second blade arrangement have an overlapping rotation region along the drive shaft, the method further comprises in the overlapping region alternately scraping away unhardened concrete by using the first blade arrangement and the second blade arrangement.

[0030] In an embodiment, the blade assembly comprises helical shaped blades.

[0031] In an embodiment of the digging apparatus, the digging apparatus comprises a blade arrangement comprises multiple blade elements configured to push loosened unhardened concrete towards the first end or the second end of the drive shaft.

[0032] In an embodiment of the digging apparatus, the two or more blade arrangements are provided with elements having a V-shaped outer edge and a first pushing side configured to move loosened unhardened concrete toward the first end and a second pushing side configured to move loosened unhardened concrete in toward the second end when the drive shaft is rotating in the drive direction.

[0033] In an embodiment of the digging apparatus, the digging apparatus further comprises a first circular disc attached to the first end and a second circular disc attached to the second end. In a further embodiment, the peripheral edge of the first and second circular disc is located at a distance from the axis of rotation that is smaller than the distance between the outer peripheral edge of blade arrangements and the axis of rotation of the drive shaft. In a further embodiment, a blade arrangement abutting the first circular disc and having a pushing side configured to move loosened unhardened concrete in the direction of the second end comprises a protrusion which is located in a plane defined by the circular disc, advantageously, the protrusion is located exterior the first circular disc.

[0034] In an embodiment of the digging apparatus, the guide plate comprises an opening providing a passage for discharging loosened unhardened concrete from the digging tool.

[0035] In an alternative embodiment of the digging apparatus, the guide plate is configured to release loosened unhardened concrete in front of or behind the digging apparatus. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] These and other aspects, properties and advantages will be explained hereinafter based on the following description with reference to the drawings, wherein like reference numerals denote like or comparable parts, and in which:

[0037] Fig. 1 illustrates a perspective view of an embodiment of a digging tool;

[0038] Fig. 2 illustrates a perspective view of the embodiment of the digging tool from another front view direction;

[0039] Fig. 3A illustrates front view of the digging tool;

[0040] Fig. 3B illustrates a top view of the digging tool;

[0041] Fig. 3C illustrates a side view of the digging tool;

[0042] Fig. 3D illustrates a bottom view of the digging tool;

[0043] Fig. 3E illustrates a rear view of the digging tool;

[0044] Fig. 4 schematically illustrates a combination of a digging tool and discharge arrangement;

[0045] Fig. 5 illustrates a front view of the embodiment shown in Fig. 1 ;

[0046] Fig. 6 schematically illustrates a side view of an alternative embodiment to discharge loosened unhardened concrete; and,

[0047] Fig. 7 schematically illustrates a front view of a specific type of concrete slab provided with a channel dig out with the digging tool.

[0048] DETAILED DESCRIPTION

[0049] Figs. 1 - 5 illustrate an embodiment of a digging tool 120. The digging tool is configured to dig an elongated channel 103 in a layer of unhardened concrete which is obtained by a substantially horizontal slip casting process. In a substantially horizontal slip casting process concrete mix is fed into a mold through a delimited cross section moving progressively in the casting process so as to form a concrete product of a desired shape and which a desired cross section. In Fig. 1 , a section of a hollow core slab 100 is shown. A hollow core slab, also known as a voided slab, hollow core plank or simply a concrete plank is a precast slab of prestressed concrete typically used in the construction of floors in apartment buildings. The precast concrete slab has tubular voids 106 extending the full length of the slab, typically with a diameter equal to the 2 / 3-3 / 4 the thickness of the slab. The process involves extruding wet concrete along with prestressed steel wire rope from a moving mold. After the concrete of the slab has cured, the continuous slab is cut to required lengths by a large diamond circular saw. Fig. 7 illustrates a hollow core slab with hollow cores in the upper half of the concrete slab. It should be noted that the digging tool disclosed in the present application may also be used for digging elongated channels in a layer of unhardened concrete without hollow cores. Fig. 1 illustrates a digging tool which digs an elongated channel with a width defined by two neighbouring tubular voids. The subject technology is not limited to elongated channels with such a width of an integer number of voids and may be used to dig elongated channels in unhardened concrete with any suitable width. In Fig. 1 the moving direction A of the digging tool to obtain the elongated channel is parallel to the length axis of the tubular voids. It should be noted that the digging tool may be used to dig channel in any angle with respect to the length axis of the concrete slab, even perpendicular to the length axis of the concrete slab.

[0050] The digging tool 120 comprises a drive shaft 122 having an axis of rotation 122C and a drive direction around the axis of rotation, a blade assembly attached to the drive shaft between a first end 122A and second end 122B of the drive shaft, two circular disks 132A, 132B located at both ends of the blade assembly, and a guide plate 128. In view of the moving direction of the digging tool, the guide plate is located behind the drive shaft, the blade assembly and the circular disks.

[0051] The blade assembly comprises two blade arrangements 124, 126 attached to the drive shaft. Each of the two blade arrangements comprises a helical shaped blade. The helical structure of the two blade arrangements allows the blades to form a cylindrical shape when they are rotated around the shaft. Each blade arrangement provides an outer peripheral edge 124A, 126A configured to make a cut in unhardened concrete and provides a pushing side 124B, 126B configured to move unhardened concrete in the direction of the first end or the second end when the drive shaft is rotating in the drive direction. A first blade arrangement 124 of the two blade arrangements extends from the first end 122A into the direction of the second end 122B. The first blade arrangement comprises an outer peripheral edge 124A configured to scrap unhardened concrete away and a pushing side 124B configured to move loosened unhardened concrete in the direction of the second end and away from the first end when the drive shaft is rotating in the drive direction. The outer peripheral edge forms a helix around the drive shaft. A second blade arrangement 126 of the two blade arrangements extends from the second end 122B into the direction of the first end 122A and comprises an outer peripheral edge 126A configured to scrap unhardened concrete away and a pushing side 126B configured to move loosened unhardened concrete in the direction of the first end and away from the second end when the drive shaft is rotating in the drive direction. The first blade arrangement and second blade arrangement have an overlapping rotation region along the drive shaft. In the overlapping region the first blade arrangement and the second blade arrangement alternately scrap away unhardened concrete in the direction of the first end and the second end. As a result, the loosened unhardened concrete is kept in this region until the loosened unhardened concrete left space in the digging tool to be collected in a collection chamber of a discharge arrangement (not shown in Fig, 1).

[0052] The guide plate 128 extends from the first end to the second end and is configured to guide loosened unhardened concrete pushed forward by the rotating pushing sides of the blade arrangement to a collection chamber of a discharge arrangement (not shown in Fig.1). In operation, there is a small gap between the inner surface of a lower part of the guide plate and the outer peripheral edges of the blade assembly to allow the pushing sides of the blade assemble to move the loosened unhardened concrete along the inner surface of the guide plate. The distance between the inner surface of the guide plate and the outer peripheral edges of the blade assembly is in the range of 0.5 - 10 mm, preferably in the range of 0.7 - 5 mm, more preferably in the range of 1 - 3 mm. In the present embodiment, the guide plate comprises an opening 30 (not visible in Fig. 1) providing a passage for loosened unhardened concrete to a collection chamber of a discharge arrangement (not shown) located behind the digging tool.

[0053] A collection chamber of discharge arrangement can be any concrete receiving space of any device suitable for discharging loosened unhardened concrete. This may include a removable container that is replaced with an empty one when full. It can also refer to the supply side of a conveyor device that transports the concrete via a conveyor belt or auger to the feeder hopper of a slip casting machine.

[0054] The digging tool 120 may be attached to any type of displacement device, e.g. a robot arm, that allows the axis of rotation of the digging tool to move parallel along the upper surface 102 of the slab 100 in any direction to form the elongated channel and to change the height of the axis of rotation to provide an elongated channel with the desired depth.

[0055] The digging tool 120 further comprises a first circular disc 132A and a second circular disc 132B. The first circular disc 132A is attached to the first end of the drive shaft and the second circular disc 132B is attached to the second end of the drive shaft. The first circular disc and the second circular disc may have a radius corresponding to the radius of the cylinder formed by the outer peripheral edges of the blade assembly when rotating around the axis of rotation. In this case, the outer peripheral edges of the circular discs function as cutting members to form sidewalls of the elongated channel. Furthermore, the circular discs support the formed sidewalls so that they do not collapse while the digging tool passes the just formed sidewall. In addition, the circular discs prevent parts of loosened unhardened concrete from hitting and damaging the sidewall that has just been formed. A pushing side of a blade arrangement should abut a circular disc to ensure that unhardened concrete on the side of the circular disc facing the blade arrangement is pushed away from the circular disc.

[0056] In the embodiment shown in the drawings, the circular discs has a radius which is smaller than the radius of the cylinder formed by the outer peripheral edges of the blade assembly when rotating around the axis of rotation. The second blade arrangement 126 abuts the second circular disc 132B and has a pushing side configured to move loosened unhardened concrete in the direction of the first end 122A of the drive shaft 122. The end of the second blade arrangement 126 touching the second circular disc comprises a protrusion 126C which is located in a plane defined by the second circular disc or, in other words, in a plane defined by the second circular disc and located outside the circular disc adjacent to an outer peripheral edge 132B’ of the second circular disc 132B. In this embodiment, the protrusion functions as a cutting member configured for making a cut in the unhardened concrete and simultaneously as a pushing member with a pushing side pushing the unhardened concrete away from the second circular disc 132B in the direction of the first circular disc 132A.

[0057] During one rotation of the drive shaft 122, the distal end of the protrusion 126C makes first a cut in the unhardened concrete to form the side wall of the elongated channel and subsequently the outer peripheral edge 126A of the blade arrangement scraps unhardened concrete away from the first circular disc to form the bottom of the elongated channel 103. Simultaneously, the pushing side 126B of the blade 126 moves loosened unhardened concrete in the direction of the guide plate 128. In this embodiment, the circular disc supports the formed sidewalls so that they do not collapse while the digging tool passes the just formed sidewall. And in addition, the circular discs prevent parts of loosened unhardened concrete from hitting and damaging the sidewall that has just been formed.

[0058] Fig. 2 illustrates a perspective view of the embodiment of the digging tool in Fig.1 from another front view direction. From this figure can be seen that the first blade arrangement 124 comprises an auger blade structure with a winding in a first winding direction and the second blade arrangement 126 comprises an auger blade structure with a winding in a second winding direction which is opposite the first winding direction. Furthermore, an opening 130 in the guide plate is visible.

[0059] Fig. 2 makes also clear that the pushing side 124B of the first blade arrangement 124 faces the pushing side 126B of the second blade arrangement 126. Furthermore, the distance between the pushing blades of the first and second blade arrangement is minimal at the free ends 124D, 126D of the blade arrangement 124, 126. When moving the digging tool and rotating the blade arrangements in the drive direction, the outer peripheral edge of the first blade arrangement 124 and second blade arrangement 126 scrap unhardened concrete away in front of the digging tool. The pushing sides force the loosened unhardened concrete between facing pushing sides to move between the between the pushing sides to move between the pushing sides in the drive direction to the guiding plate. Due to gravity forces the loosened unhardened concrete is collected at the bottom of the space between pushing sides. As, during rotation of the blades, the distance between facing pushing side’s decreases to the minimal distance between a free end and neighbouring pushing side, loosened unhardened concrete collected between the free end cannot pass the gap between the free end and the pushing side next to the free end in time. As a result, a part of the loosened unhardened concrete is moved in upward direction along the inner surface of the guide plate and pushed through the opening 130 to discharge the digging tool.

[0060] Fig. 3A illustrates front view of the digging tool. In this figure can be seen that the lower edge 128B of the guide plate 128 is at the same level as the lowest point of the outer peripheral edge of the first and second blade arrangement 124, 126. As a result, the guide plate functions as a scoop and all loosened unhardened concrete is pushed on the inner surface of the guide plate and the pushing sides of the blade arrangements will move the loosened concrete upward in the direction of the opening 130. The opening has a quadrilateral shape with a small width at the bottom of the opening and a large width at the top of the opening. It should be noted that shaped and dimensions of the opening is not an essential part of the invention, and may therefore be any shape suitable for the desired application.

[0061] Fig. 3B illustrates a top view of the digging tool. This figure clearly shows that the first blade arrangement 124 and the second blade arrangement 126 are augershaped blades with opposite winding directions. It can also be seen that they have an overlapping part because end sections of the blades are twisted together, so to speak.

[0062] Fig. 3C illustrates a side view of the digging tool of the first end. Shown is the direction of rotation 122D of the drive shaft 122 around the axis of rotation 122C. It can be seen that the radius of the out peripheral edge 132A’ of the first circular disk 132A, provided at the first end 122A of the drive shaft 122, is smaller than the radius of the helix formed by the outer peripheral edge 124A of the first blade arrangement 124. In this figure by dashed lines, the front edge 124E and rear edge 124D of the first blade arrangement 124 are indicated. It can be estimated that the first blade arrangement is an auger blade having a winding of about 240°. As the first blade arrangement does not have an auger blade with a full winding, the second blade arrangement 126 can be seen through the gap between the outer peripheral edge 132A’ of the circular disk 132 and the guide plate 128. It should be noted that the characteristics of the auger-shaped blade, such as diameter of the outer peripheral edge, pitch and winding angle of the auger blade, depend on the application of the digging tools. Furthermore, Fig. 3C discloses that the protrusion 124C of the first blade arrangement 124 is located in driving direction 122D before the front edge 124E of the blade of the first blade arrangement 124.

[0063] The winding angle, the rotation speed and the moving speed of the digging tool determine the direction in which the unhardened concrete is scraped away and the loosened unhardened concrete pushed sideways.

[0064] Fig. 3D illustrates a bottom view of the digging tool. This figure discloses that the lower edge 128B of the guide plate is in moving direction of the digging tool located behind the axis of rotation 122C.

[0065] Fig.3A, 3B and 3C show that the lower edge 128B of the guide plate 128 is parallel to the axis of rotation 122C. Moreover, the outer peripheral edge of the blade arrangements always pass the lower edge 128B at an angle. Since the angle is greater than 45 degrees, there is a very small probability that a stone of the loosened unhardened concrete get stuck between the lower edge and the outer peripheral edge, stopping the rotation of the digging tool.

[0066] Fig. 3E illustrates to rear view of the digging tool showing a possible position of the quadrilateral shaped opening 130 in the guide plate 128. The location of the opening should allow the pushing sides of the blade arrangements to discharge loosened unhardened concrete from the space in the rotating space between the elements attached to drive shaft through the opening 130.

[0067] Fig. 4 schematically illustrates combination of a digging tool and discharge arrangement while digging an elongated channel 103 in an unhardened concrete slab as shown in Fig. 1. The drive direction 122D is anti-clockwise and the digging direction A is from the right to the left in Fig. 4. In front of the digging tool there is a tubular void 106. Behind the digging tool there is the elongated channel 103. The elongated channel 103 has a width defined by two neighbouring tubular voids. The digging tool digs an elongated channel which bottom is located above the bottom of the tubular voids. In Fig. 4 the part of the separation wall between the two tubular voids which is not removed by the digging tool forms a ridge 108. The grooves 104 at both sides the ridge are filled with loosened unhardened concrete. The lower edge 128B of the guide plate defines the digging depth and consequently the height of the ridge 108. As the grooves adjacent to the ridge 103 are filled with unhardened concrete during the digging process, the lower edge 128B also determines the thickness of the concrete layer between the bottom of the elongated channel 103 and the bottom side of the concrete slab. The part of the loosened unhardened concrete that is not needed to fill the grooves 104 is being scooped by the guide plate 128 and the pushing sides of the blade arrangements push the loosened unhardened concrete upward along the inner surface of the guide plate 128 to the opening 130 in the guide plate. From the description above, it is clear that the guide plate does not loosen unhardened concrete; it does not scrape it away but only processes concrete that has already been loosened by the blade arrangements. The loosened unhardened concrete will leave the space 150 in the digging tool between the blades of the blade arrangement and fall in the collection chamber 160 of the discharge arrangement 170. The discharge arrangement can be any type of device suitable to store an amount of loosened unhardened concrete and optionally to move it away from the digging tool for reuse. This can vary from a container coupled to the digging tool which can easily be emptied to a container with at its bottom a transport auger or conveyor belt to transport the loosened unhardened concrete directly to another device or storage.

[0068] Fig. 5 illustrates a front view of the embodiment shown in Fig. 1. In operation of the digging tool 120, the outer peripheral edges 124A, 126A will scrap unhardened concrete before the digging tool and the sides 124B and 126B will push the loosened unhardened concrete downward in the direction of the lower edge 128B of the guide plate 128. The loosened unhardened concrete will first fill the part 104 of the tubular void 106 below the blade arrangements 124, 126 located before the lower edge 128B. When said part is filled the remaining loosened unhardened concrete will be pushed on the guide plate and moved to the opening 130 in the guide plate. Only an upper part of the concrete wall between the tubular voids on which location the elongated channel is formed is scraped away. The lower part 108 forms a ridge between the grooves that are filled with loosened unhardened concrete.

[0069] Fig. 6 schematically illustrates a side view of an alternative embodiment to discharge loosened unhardened concrete. In this embodiment, the guide plate 128 does not have an opening. The guide plate above the blade arrangements is extended to the front side of the digging tool. Due to the rotation speed of the digging tool the loosened unhardened concrete is accelerated such that the loosened concrete is thrown in a collection chamber 160 of a discharge arrangement 170. This embodiment has the advantage over the embodiment with opening 130 that the possibility of contaminating the formed elongated channel 103 with loosened concrete is significantly reduced. Fig. 7 schematically illustrates a front view of a specific type of concrete slab provided with a channel dig out with the digging tool as shown in Fig. 6. The concrete slab comprises tubular voids in the upper half of the concrete slab 100. An elongated channel 103 is formed at the location of two neighbouring tubular voids. In this embodiment, the bottom of the elongated channel is at the same level as the bottom side of the tubular voids. Now, all loosened unhardened concrete that has to be removed to form the elongated channel is removed by the digging tool.

[0070] In the embodiment described above, the first blade arrangement and second blade arrangement comprises a contiguous blade. In an alternative embodiment, the first and second blade arrangement is composed of a number blade parts wherein the outer peripheral edges of the blade parts of a blade arrangement together are on the same helix.

[0071] In an alternative embodiment, a blade arrangement comprises two or more auger blade structures along the same portion of the drive shaft. In this embodiment, the blade arrangement scraps a thin layer of unhardened concrete from the slab twice in one revolution.

[0072] It is also possible to form a blade arrangement with a multitude of relative small blades which outer distal edge has an angle corresponding to the angle of auger blade with respect to the rotation plane. When the outer distal edges of all small blades together forming the first or second blade arrangement provide a contiguous distal edge along the axis of rotation, such a blade arrangement can also perform the functions of the first and second blade arrangements describes above.

[0073] In an alternative embodiment of the digging tool comprises a multitude of blade arrangements with a V-shaped blade with V-shaped outer edge and a first pushing side configured to move loosened unhardened concrete toward the first end and a second pushing side configured to move loosened unhardened concrete in toward the second end when the drive shaft is rotating in the drive direction. In this embodiment, the connection line where the first pushing side and second pushing side come together form a cutting edge configured to make a cut in the unhardened concrete. In operation, a V-shaped blade function as a wedge that first makes a cut in the unhardened concrete, the V- shaped outer edge scrapes a layer of unhardened concrete away and the first pushing side and second pushing side pushes the loosened unhardened concrete to the left and right of the cut made be the cutting edge of the V-shaped blade. Preferably, the V-shaped blades are distributed along the axis of rotation such that the V-shaped outer edges allow the blade assembly to form a contiguous cylindrical shape when they are rotated around the axis of rotation. Advantageously, the first pushing side and second pushing side of neighbouring V-shaped blades have an overlapping region wherein the first and second pushing side rotate in the same plane. This improves the discharge of loosened unhardened concrete from the digging tool. To reduce the maximum power needed to rotate the blade assembly, the V-shaped blade are distributed around the axis of rotation such that when rotating the blade assembly, the total length of the outer edges being in contact with the concrete slab is almost independent of the angle of rotation of the blade assembly. As a result, the power needed to rotate the blade assembly varies minimally.

[0074] From the embodiments described and shown in the figures, a person skilled in the art will recognize that the blades comprise a trailing part and a leading part. The trailing part is the section of the blade that first comes into contact with the concrete, while the leading part is the section that contacts the concrete last.

[0075] A left pushing blade, which pushes concrete to the left, and a right pushing blade, positioned to the left of the left pushing blade, together form a V-shaped space with a narrow open bottom.

[0076] During use, the concrete is moved to the bottom of the V-shaped space. The narrow open bottom creates resistance for the loosened concrete. Consequently, a portion of the concrete passes through the narrow open bottom, while the remaining part is moved by the rotation of the blades along the inner surface of the guiding plate towards the collection chamber. An advantage of the gap between the left and right pushing blades is that the blade assembly accumulates concrete particles more slowly compared to a design without an open gap between the blades. Furthermore, the gap facilitates cleaning and the removal of stones from the blade assembly. This principle applies to both the blade assembly with helical blades and the blade assembly with V-shaped blades.

[0077] It is clear to the skilled person that the gap should not be too wide; otherwise, almost all the loosened concrete will pass through the gap, leaving only a small part to be discharged along the guiding plate. Conversely, the gap should not be too narrow, as gravel could quickly become stuck between the blades. Therefore, the skilled person will preferably choose a gap width that is slightly wider than the maximum grain size of the gravel used in the concrete.

[0078] While the invention has been described in terms of several embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent to those skilled in the art upon reading the specification and upon study of the drawings. The invention is not limited to the illustrated embodiments. The scope of protection is defined by the appended claims.

Claims

CLAIMS:

1. Method for fabricating a concrete slab in a substantially horizontal slip casting process, in which method concrete mix is fed into a mold through a delimited cross section moving progressively in the casting process so as to form a concrete product of a desired shape, the method comprising loosening unhardened concrete to be removed from the surface (102) of an unhardened concrete element (100) by means of a digging tool (120) to obtain loosened unhardened concrete, wherein the digging tool moves in a digging direction (A) substantially parallel to the surface of the concrete element (102), and discharging loosened unhardened concrete from the concrete element (102) to form an elongated channel (103) with a width determined by the digging tool; characterized in that, the digging tool comprises: a drive shaft (122) having an axis of rotation (122C) and a drive direction around the axis of rotation, a blade assembly attached to the drive shaft between a first end (122A) and second end (122B) of the drive shaft, the blade assembly comprises two or more blade arrangements (124, 126) attached to the drive shaft, the blade arrangements providing outer peripheral edges (124A, 126A) configured to scrap unhardened concrete away and providing pushing sides (124B, 126B) configured to move unhardened concrete in the direction of the first end or the second end when the drive shaft is rotating in the drive direction; and, a guide plate (128) extending from the first end to the second end configured to guide loosened unhardened concrete to a collection chamber (160) of a discharge arrangement (170); wherein the method comprises: moving the digging tool in a digging direction; rotating the drive shaft around the axis of rotation in the drive direction; loosening unhardened concrete by simultaneously scraping away a layer of unhardened concrete using the outer peripheral edges (124A, 126A) and pushing by using pushing sides unhardened concrete towards the first end or the second end by rotating the blade assembly around the axis of rotation; moving loosened unhardened concrete along an inner surface of the guide plate into the direction of the collection chamber (160) of a discharge arrangement (170) by rotating the pushing sides (124B, 126B) around the axis of rotation.

2. The method according to claim 1 , wherein the blade assembly comprises at least one cylindrical rotation area around the drive shaft provided with an end part of a pushing blade which is configured to push loosened unhardened concrete in the direction of the first end of the drive shaft and an end part of a pushing blade which is configured to push loosened unhardened concrete in the direction of the second end, wherein the method further comprises moving loosened unhardened concrete in the at least one cylindrical rotation area alternately to the first end and to second end of the drive shaft.

3. The method according to any of the claims 1 - 2, wherein the blade arrangement comprises: a first blade arrangement (124) and a second blade arrangement (126) both attached to the drive shaft between a first end (122A) and second end (112B) of the drive shaft; the first blade arrangement (124) extending from the first end (122A) into the direction of the second end (122B), providing an outer peripheral edge (124A) configured to scrap unhardened concrete away and providing a pushing side (124B) configured to move loosened unhardened concrete in the direction of the second end when the drive shaft is rotating in the drive direction; and, the second blade arrangement (126) extending from the second end (122B) into the direction of the first end (122A), providing an outer peripheral edge (126A) configured to scrap unhardened concrete away and providing a pushing side (126B) configured to move loosened unhardened concrete in the direction of the first end when the drive shaft is rotating in the drive direction; wherein the method comprises: moving loosened unhardened concrete away from the first end by rotation of the first blade arrangement around the axis of rotation; and, moving loosened unhardened concrete away from the second end by rotation of the second blade arrangement around the axis of rotation.

4. The method according to claim 3, wherein the first blade arrangement and second blade arrangement have an overlapping rotation region along the drive shaft, the method further comprises in the overlapping region alternately scraping away unhardened concrete by using the first blade arrangement and the second blade arrangement.

5. The method according to any of the claims 1 - 4, wherein the blade assembly comprises helical shaped blades.

6. The method according to any of the claims 1 - 5, wherein a blade arrangement comprises multiple blade elements configured to push loosened unhardened concrete towards the first end or the second end of the drive shaft.

7. The method according to any of the claims 1 - 2, wherein the two or more blade arrangements are provided with a V-shaped outer edge and a first pushing side configured to move loosened unhardened concrete toward the first end and a second pushing side configured to move loosened unhardened concrete in toward the second end when the drive shaft is rotating in the drive direction.

8. The method according to any of the claims 1 - 7, wherein the digging tool further comprises a first circular disc (132A) attached to the first end and a second circular disc (132B) attached to the second end; the method further comprises: protecting the side walls of the elongated channel from being damaged by concrete parts jumping around between rotating pushing blades by the first and second circular disc.

9. The method according to claim 8, wherein the peripheral edge of the first and second circular disc is located at a distance from the axis of rotation that is smaller than the distance between the outer peripheral edge of blade arrangements and the axis of rotation of the drive shaft.

10. The method according to claim 8 - 9, wherein a blade arrangement abutting the first circular disc and having a pushing side configured to move loosened unhardened concrete in the direction of the second end comprises a protrusion which is located in a plane defined by the circular disc.

11. The method according to claim 10, wherein the protrusion is located exterior the first circular disc.

12. The method according to any of the claims 1 - 11 , wherein the guide plate comprises an opening providing a passage for discharging loosened unhardened concrete from the digging tool; wherein the method comprises: moving loosened unhardened concrete along the guide plate to the opening to discharge loosened unhardened concrete from the digging tool by rotation of the blade assembly around the axis of rotation.

13. The method according to any of the claims 1 - 11 , wherein the method comprises: moving loosened unhardened concrete along the guide plate to discharge loosened unhardened concrete from the digging tool by rotation of the blade assembly around the axis of rotation in a collection chamber (160) of a discharge arrangement (170) located in front of the digging tool.

14. A digging apparatus for providing an elongated channel (103) in a surface of an unhardened concrete element, comprising all technical features of a digging tool according to any of the claims 1 - 13.

15. Digging apparatus for providing an elongated channel (103) in a surface of an unhardened concrete element, comprising: a drive shaft (122) having an axis of rotation (122C) and a drive direction around the axis of rotation, a blade assembly attached to the drive shaft between a first end (122A) and second end (122B) of the drive shaft, the blade assembly comprises two or more blade arrangements (124, 126) attached to the drive shaft, the blade arrangements providing outer peripheral edges (124A, 126A) configured to scrap unhardened concrete away and providing pushing sides (124B, 126B) configured to move unhardened concrete in the direction of the first end or the second end when the drive shaft is rotating in the drive direction; and, a guide plate (128) extending from the first end to the second end configured to guide loosened unhardened concrete to a collection chamber (160) of a discharge arrangement (170).

16. Digging apparatus according to claim 15, wherein the blade assembly comprises at least one cylindrical rotation area around the drive shaft provided with anend part of a pushing blade which is configured to push loosened unhardened concrete in the direction of the first end of the drive shaft and an end part of a pushing blade which is configured to push loosened unhardened concrete in the direction of the second end.

17. Digging apparatus according to any of the claim 15 - 16, wherein a first blade arrangement (124) and a second blade arrangement (126) both attached to the drive shaft between a first end (122A) and second end (112B) of the drive shaft; the first blade arrangement (124) extending from the first end (122A) into the direction of the second end (122B), providing an outer peripheral edge (124A) configured to scrap unhardened concrete away and providing a pushing side (124B) configured to move loosened unhardened concrete in the direction of the second end when the drive shaft is rotating in the drive direction; and, the second blade arrangement (126) extending from the second end (122B) into the direction of the first end (122A), providing an outer peripheral edge (126A) configured to scrap unhardened concrete away and providing a pushing side (126B) configured to move loosened unhardened concrete in the direction of the first end when the drive shaft is rotating in the drive direction.

18. Digging apparatus according to claim 17, wherein the first blade arrangement and second blade arrangement have an overlapping rotation region along the drive shaft, the method further comprises in the overlapping region alternately scraping away unhardened concrete by using the first blade arrangement and the second blade arrangement.

19. Digging apparatus according to any of the claims 15 - 18, wherein the blade assembly comprises helical shaped blades.

20. Digging apparatus according to any of the claims 15 - 19, wherein a blade arrangement comprises multiple blade elements configured to push loosened unhardened concrete towards the first end or the second end of the drive shaft.21 . Digging apparatus according to any of the claim 15 - 16, wherein the two or more blade arrangements are provided with elements having a V-shaped outer edge and a first pushing side configured to move loosened unhardened concrete towardthe first end and a second pushing side configured to move loosened unhardened concrete toward the second end when the drive shaft is rotating in the drive direction.

22. Digging apparatus according to any of the claims 15 -21 , wherein the digging apparatus further comprises a first circular disc (132A) attached to the first end and a second circular disc (132B) attached to the second end.

23. Digging apparatus according to any of the claims 15 - 22, wherein the guide plate is configured to release loosened unhardened concrete in front of or behind the digging apparatus.

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